explanation for conspicuous traits (bright colors, horns)
Occurs because females produce few and large gametes and males produce many small sperm. (Creates automatic conflict)
Also called intrasexual selection.
Often compete for mating opportunities through visual displays or ornaments.
Some engage in fights and possess weapons
These types of traits are called secondary sexual characteristics.
Directional selection increases the size, weaponry, or display features which leads to an arms race.
Escalation is limited by ecological factors.
In some species with internal fertilization, seminal fluid of a mating male reduces the sexual attractiveness of females to other males.
Some species reduce receptivity
Hypotheses for Male Choice
Direct benefit to choosy females
Indirect benefits to choosy females
Males provide direct benefit to female or offspring (nutrition, superior territory for resources, parental care)
Competitive sex evolves traits that exploit pre-existing bias that the choosy sex already possesses
(Female guppies have affinity for male orange guppies b/c that is color of preferred fruit)
Males do not provide for offspring and only contribute genes.
Runaway sexual selection
(indirect benefit) Sons of females that choose a certain male trait have improved mating success b/c they inherit the trait that made their fathers appealing to their mothers.
Good Genes Model
(indirect benefit) Preferred male traits indicate higher viability, which is inherited by the offspring of the female who choose good males
theory of natural selection based on individual advantage.
Why is group selection NOT a likely reason altruism occurred
Individuals that cooperate would secure fewer mates and have fewer offspring. Cheaters would flourish and selection would be weak.
Four classes of individual selection hypotheses attempting to explain altruistic traits
Manipulation, Individual advantage, Reciprocation, Kin Selection
ex. vampire bats live in groups. Members that have fed successfully will sometimes feed regurgitated blood to other members of the group that need it. Recipients will reciprocate at other times.
This type of cooperation evolves rarely because cheaters are often possible.
Individuals must dispense benefits more often to kin than to non-kin.
Advantages and disadvantages of cooperation are measured by fitness (contribution of genes to subsequent generations)
Selection based on inclusive fitness is kin selection
the effect of fitness of an allele on both the individual that has it (direct fitness)
the fitness of other individuals that share the allele (indirect fitness)
An individual performs an act that benefits another individual but incurs a cost to itself
An altruistic trait can increase in frequency if the benefit (b) received by the donor's relatives, weighted by their relationship (r) to the donor, exceeds the cost (c) of the trait to the donor's fitness
rb > c
Hamilton's Rule coefficients
r = coefficient of relationship
ex. r = .5 between mother and daughter
The benefit must be greater the more distantly related the donor and the recipient are.
the alleles that would allow aunts to care for nieces would spread only if benefit is more than four times the cost of the care.
Donor dispenses aid because the donor is being manipulated by the recipient.
ex. a parasitic nestling solicits aid from the host parents by mimicking the host's children. The nest parasite may end up destroying the host's own offspring.
Can occur within species species also (extra pair copulations)
Cooperative behavior may evolve b/c it is advantageous to the individual
Joining a flock or herd is advantageous for safety.
This increases compactness of the group.
young are reared not just by parents.
In birds that display this behavior, young males that are prevented from breeding by competition for mates lack territory.
These young males help their parents rear additional offspring.
Most extreme for of altruism is in eusocial animals.
(mole rats only eusocial mammal)
some workers are sterile or near sterile
showing an advanced level of social organization, in which a single female or caste produces the offspring and nonreproductive individuals cooperate in caring for the young.
Females from fertilized eggs (diploid)
Makes from unfertilized eggs (haploid)
Sisters are more related to each other (.75) than to their mother (.5), and less to their brother (.25)
Inclusive fitness of female is greater if she devotes energy to raising reproductive sisters (queens) than by having offspring of her own.
Kin Selection is responsible for eusociality evolving multiple times
Increases the survivability of offspring,
Has costs: Require expenditure of time and energy that could be allocated towards further reproduction or finding additional mates
Sometimes the fitness of an individual is enhanced by killing young members of the same species.
ex. Male lions kill the offspring of their mates once they replace the previous mate. That male can then father his own children b/c the female will become reproductive sooner.
Sometimes parents kill offspring to regulate brood size.
fitness is proportional to the # of surviving offspring (eggs x proportion that survive)
If siblings share an environment they may actively fight for resources.
Larger individuals may kill smaller ones
normal in eagles
Parental care may reduce the production of future offspring.
Offspring will try to obtain more resources from a parent than it is optimal for a parent to give
(r = .5 in siblings and r = 1 in itself)
The study of interactions of organisms with one another and with their physical environment
The interaction of environmental factors and intrinsic characteristics (life history traits) and their effect on populations
3 Characteristics of population ecology
Population range (distribution), Pattern of spacing of individuals, change in population size through time
Where the species is located. Can be large or small and ranges may shift in response to climate change or b/c of human mediation .
Pattern of Spacing
May be randomly spaced, uniformly spaced or clumped.
Randomly spaced- is unlikely to be common in nature
Uniform spacing may result from defended territories
Clumped Spacing is common and results from distribution of resources or social interactions
Change in Population Size (Metapopulation)
Metapopulation- network of distinct populations that interact with one another by exchanging individuals.
Extent of change depends on dispersal rates
Some populations may go extinct then be recolonized.
Source-sink metapopulation- Source populations continually send out dispersers into poorer habitats (sinks)
Study of population size and age structure through time.
Dynamics of populations inherent in definition. Accounts for # of adults, juveniles, young, birth rates and death rates
Number of individuals in each statistical group
Influences growth rate through #of offspring produced vs mortality
Depicts the fate of a cohort (group of individuals) from birth until death
shows number of offspring produced and number of individuals that die each year
The percentage of an original population that survives to a given age.
Type I- Low mortality rate early in life, high mortality later in life.
Type II- Individual are equally likely to die at any age
Type III- High Mortality rate early in life, low mortality later in life
Cost of Reproduction
Reduction in future reproductive potential resulting from current reproductive effort.
Increased reproduction correlates with high mortality rate.
Trade-off between # offspring and investment per offspring.
Trade-off between age at first reproduction and life span
long lived species put off reproduction longer than short-lived species
Trade-off between age and fecundity (ability of producing many offspring)
semelparity- single, large reproductive even
ex. annual plants, insects, salmon
Iteroparity- offspring produced several times over man seasons
Models of Population Growth
defined as r = (b - d) + (i - e)
r = rate of population increase
b = birth rate
i = movement into an area (immigration)
e = movement out of an area (emigration)
When no limits are placed on a population, growth is exponential dN/dt = rN
(rate of change/time)
the maximum number of individuals that an environment can support. A population at carrying capacity is said to be at equilibrium.
K = carrying capacity
Growth rate can not exceed capacity
As a population increases, reproductive rates decline and mortality rates increase.
ex. predators target common prey species
Population growth rates may be effected by population size.
Rate of population growth limited by something unrelated to population size.
ex. cold winters, droughts, storms etc.
Organisms living together in a location are members of a community.
Over time different species adjust to living with each other and evolve together.
Competition, Cooperation, and predator-prey interactions all play key roles in communities.
How Communities are Characterized
Characterized by species richness (# of species) or by the amount of energy produced (primary productivity)
Interactions among community members (predation, mutualism, etc.) affect the population biology of individual species.
A community is simply an aggregation of species that happen to occur together.
Species appear and disappear independently across space and time.
i.e. tree species density along a moisture gradient, each tree as unique response to moisture gradient.
Communities are an integrated unit that can function as a "superorganism"
More than the sum of its parts.
Communities stay the same through space and time until environmental conditions are different enough to support a different community.
i.e. plant community changes along a place where the environment changes abruptly
All the ways an organism uses the resources in its environment.
i.e. food, temperature range, moisture range
Some species cannot occupy entire niche due to interspecific competition or competition between resources
The entire niche that a species is capable of using
The actual set of environmental conditions in which the species establishes a stable population.
Interspecific interactions may make the realized niche smaller than the fundamental niche.
Causes of Niche Restriction
Predators, absence of another species.
If 2 species using the same resources. the more efficient species will eliminate the weaker one.
Subdividing a niche between competitors, splitting resources
Predation- the consuming of one organism by another. Predators have large effects on prey population. Prey can also effect predator populations
One of first mathematically sound models of predator-prey reactions (foxes and rabbits)
dR/dt = rR - aRF
dF/dt = bRF - mF
R is density of prey
F is the density of predators
r is the intrinsic rate of prey population increase
a is the predation rate coefficient
b is the reproduction rate of predators per one prey eaten
m is the predator mortality rate
bright conspicuous markings of certain distasteful or poisonous animals, which predators recognize and learn to avoid
A harmless species has evolved to mimic a toxic or poisonous species
2 Harmful species mimic one another
Species that have a large effect on the composition of communities.
ex. removal of sea otter shifted community away from kelp forest.
Primary Ecological Succession
The area begins as bare and lifeless and organisms gradually move into area.
ex. land exposed by retreating glaciers, lichens are first to colonize then break down substrate creating soil then mosses colonize in soil pockets, then hardy shrubs (alders) can hold having bacteria. Over time nitrogen accumulates in soil, acidic leaves of alders lower the pH further. Spruces are then established and forms a dense forest.
Enormous eruption in 1883. Destroyed all life on the islands. at first nothing but barren ash, after one year 1 blade of grass, after 15 years coastal vegetation appeared, by 1930 almost entirely forested.
Secondary Ecological Succession
A disturbance occurs (fire clearing) and eventually marks of the disturbance disappear. Organisms remain to recolonize.
Intermediate Disturbance Hypothesis
Communities experiencing moderate amounts of disturbance have higher species richness than those experiencing very little or a lot of disturbance.
1. in communities w/ moderate disturbances there will be many patches at different successional stages increasing the diversity in are.
2. Moderate levels of disturbance prevent communities from reaching final stage of succession where a few dominant competitors eliminate the other species.
Ecosystem consists of all organisms and non living stuff in environment.
Compounds important in moving through ecosystems: Carbon, Water, Nitrogen, Phosphorous
Carbon forms framework of all organic compounds.
Almost 20% of body wight of a human is carbon.
C02 is the most significant carbon containing compound in abiotic (nonliving) environment (.03% of atmosphere)
CO2 in water spontaneously forms bicarbonate ions (HCO3-)
Organisms converte CO2 to organic compounds (carbon fixation)
Animals eat autotrophs to build own tissue with carbon.
Dead organisms produce CO2
Carbon can be locked up in biomass or as in fossil fuel deposits.
Rapid conversions of these into CO2 creates imbalances.
All life depends on water.
The bodies of most organisms consist mainly of water.
Adult human is 60% water weight
Water determines abundance of organisms present.
water evaporates into the atmosphere directly from oceans, lakes, and rivers
In terrestrial ecosystems, 90% of water that reaches atmosphere passes through plants.
Groundwater occurs in aquifers and is important reservoir on land.
95% of freshwater in US is form of groundwater.
Important component of all proteins and nucleic acids.
It is often a limiting resource even the atmosphere is 78% nitrogen.
N2 (gas) Unusuable to plants and animals.
Plants and algae use nitrogen compounds that can be synthesized from nitrogen gas by prokaryotes. Other prokaryotes turn useable nitrogen back to nitrogen gas.
Fertilizers use NH4- ammonium with increases the amount of fixed nitrogen in the environment through the use of fertilizers in agriculture.
Required by all organisms- occurs in nucleic acids, cell membranes, and ATP for energy.
Does NOT occur as a gas and does not cycle through the atmosphere
It exists in ecosystems in oxidized form only as phosphate (PO4 3-)
Plants and animals use free phosphates in the soil or water to make organic compounds.
animals eat them and use phosphorous for themselves.
Weathering of rocks can introduce phosphates into terrestrial ecosystems and rivers carry phosphates to the ocean
creates one way flux of phosphates
Phosphates in fertilizers and detergents modify the global phosphate cycle.
Energy is never recycled in ecosystems.
Enters via sun and leaves via heat.
use light as energy source
Those that use inorganic oxidation reactions
One step in a food chain. Composed of autotrophs and heterotrophs
First level = primary producer
second level- herbivores
third level- primary carnivores (eat herbivores)
fourth level- secondary carnivores (eat carnivores)
Detritvores- Eat dead organisms
A result of the effect of geographic isolation and the likelihood of colonization and extinction.
# of species on an island reaches equilibrium.
Equilibriu is effected by the size of island and distance from mainland.
Larger islands support more species than smaller islands.
Smaller islands have higher extinction levels because population size is more limited.
Closer Islands have more species than farther islands b/c it is more difficult for species to disperse to farther islands.
The branch of biology that deals with the effects of humans on the environment and with the conservation of biological diversity.
Applied science, how to preserve species, communities, ecosystems, causes of the loss of biodiversity, develops methods for preventing species loss.
Extinction is natural. more than 99% of species are extinct. 20% of worlds biodiversity will be lost by 2050.
Historical Human Activity
Human impacts on biodiversity can be seen historically.
74-86% of megafauna extinct when humans arrived in north america
1 species per year from 1850-1950
4 species per year 1986-1990
Islands and extinction
majority of historic extinctions occur on islands.
Absence of predators, humans introduce competitors, predators, and diseases, island populations are initially small
When a species is found in one geographic area and nowhere else.
Islands are popular places, concentrated in hotspots.
Conserving endemic species protects high percentage of world's biodiversity
Human population growth in hotspots
population growth in hotspots is nearly 2x as much as rest of the world in some hotspots.
Hotspots are experiencing habitat destruction.
Hotspots are at risk in more affluent countries (so. cal)
Human population growth
currently 6.9 people growing at 1.2% per year.
Population pyramid depicts age distribution
Factors responsible for extinction
Habitat loss, Overexploitation, Species introductions
Most important cause for modern extinction.
humans cause: destruction, pollution, disruption, fragmentation
-Clearcutting harvesting, of timber
-burning tropical forest to produce grazing land
-Urban and industrial development
Application of the Species-area curve
Larger area supports more species
A 10-fold increase in land area doubles the # of species it holds.
If area is reduced by 90% only half of species will remain
Habitat may be degraded by pollution so that some species may no longer survive there.
Aquatic environments are particularly vulnerable
Some lakes in Europe and and North America have been sterilized by acid rain.
Human activity can interrupt enough to make land unusable.
Visitors to caves can disrupt bats
Loss of habitat results in lower population #'s and also fragmentation of population.
enhances edge effects
edge effects- changes in microclimate or access by nonnative species
trees on edge are more exposed to wind, sunlight.
Species that are hunted or harvested by humans are at high risk for extinction. Commercial market often leads to overexploitation
-international fur trade, valuable trees, fisheries, whaling
A natural process by which a species expands its geographic range.
-Ecological interactions may be particularly strong because species may have evolved or adjusted to the presence of one another.
-Naturally large scale colonizations have occurred
Human introduction of species
50k species introduced to US
Plants and animals transported in ballast of vessels, in nursery plants, beetle larvae in wood, seeds or spores on bottom of shoes.
Effects of introduction of species
Nonnative species cost 140 billion a year
effect human health
islands are particularly vulnerable
How an animal responds to stimuli of the environment.
i.e. detection of food in environment
How behavior works
How the sense, nerve networks, or internal state provide the physiological basis for behavior.
ex. male songbird sings during mating season due to increased testosterone binding to receptors in brain
Why a behavior evolved
How it influences the organism's reproduction or survival.
ex. male songbirds sing to attract mates (increase reproduction) or defend resources.
Controversy of behavior
Whether a behavior is determined by genes or by learning experience. (nature vs. nurture)
Both play roles
a behavior that is influenced by genes and does not depend on learning.
ex. if a goose notices an egg knocked out of its nest it will extend its neck toward the egg, get ip and roll egg back into the nest.
an external sensory stimulus that triggers a fixed action pattern
Innate releasing mechanism
neural network that detects cue, starts fixed action pattern
an exaggerated version of a stimulus to which there is an existing response tendency, or any stimulus that elicits a response more strongly than the stimulus for which it evolved.
Deals with hereditary components of behavior.
Artificial selection experiments and modern molecular genetics show genetic differences lead to behavioral differences.
selection by humans for breeding of useful traits from the natural variation among different organisms
ex. breeding fast learning rats together and slow learning rats led to two behaviorally distinct types of rats.
Identical twins separated at birth often have similarities in temperament and leisure activities.
Some behaviors appear to be controlled by single gene.
The fosB gene produces a protein that affects the neural circuitry in the hypothalamus of the brain.
Disabling the gene deactivates maternal behavior.
Not all behaviors are result of instinct, animals alter behavior after previous experiences.
decreasing responsiveness with repeated stimulation.
Learning to ignore unimportant stimuli is important for animals that live in a complex environment.
A change in behavior that involves an association between two stimuli or stimulus and a response.
two types: classical and operant conditioning
Paired presentation of two different kinds of stimuli causes the animal to form an association between the stimuli. (Pavlovian conditioning)
Pavlov presented meat powder (unconditioned stimulus) and the dog salivated (unconditioned response). If a bell was rung (unrelated stimulus) at the same time as the meat powder is presented, the dog associates the unrelated bell with the meat powder. They salivate whenever the bell is rung (Conditioned response)
Animal associates its response with either a reward or punishment.
Rats would explore a box with a lever. They would accidentally press the lever and food would appear. Eventually they learned to associate pressing it when hungry.
Involved with predator-prey interactions.
After being stung the toad learns not to eat bees.
Some animals have predispositions toward forming certain associations.
Development of Behavior
Offspring form attachments to other individuals as they mature.
the process by which certain animals form attachments during a critical period very early in life
ducklings follow their mother - do so virtually from birth - do not follow other ducks
Instinct and Learning Interact
If some birds do not hear the song of males of their species they sing poorly.
If they are exposed to another species' song they cannot learn it.
Birds have genetic template to guide them to right song.
for cuckoos, song must be innate because they do not see their parents.
Sea Otters use a rock as an anvil to break open a clam.
Japanese macaques learned to wash sand off potatoes.
Chimps were placed in room with boxes and bananas and figures how to reach bananas.
Communication plays important role in reproduction and social interactions.
Visual, acoustic, tactile, chemical
The behavior of one individual releases the behavior of another.
Long distance chemical attractants.
Insects, amphibians, birds produce species specific acoustic signals to attract mates.
Communication and group living
Information is communicated between group members as guard or alarm calls when predators approach.
Social insects can produce pheromones that trigger attack behavior.
Honeybees have complex dance that directs other bees in the hive to nectar.
deviation from vertical = angle from sun
Duration of dance indicated distance.
Vocalization of african vervet monkeys indicate different predators.
Chimps and gorillas can recognize lare # of symbols and use to communicate abstract concepts.
The study of how natural selection shapes behavior.
Adaptive significance of behavior.
Is behavior adaptive? if so how does it increase reproduction success.
Optimal forage theory
Natural selection favors individuals whose foraging behavior is as energy efficient as possible.
- Maximize energy intake while minimizing effort.
-Natural selection will only favor a behavior that maximizes energy acquisition, if the increase in energy leads to greater reproductive success.
-Optimal behavior evolved by natural selection.
- also avoidance of predators and finding mates.